Institute for Marine Resources and Ecological Studies

Ijmuiden, Netherlands

Institute for Marine Resources and Ecological Studies

Ijmuiden, Netherlands

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Cuveliers E.L.,Charles University | Volckaert F.A.M.,Charles University | Rijnsdorp A.D.,Institute for Marine Resources and Ecological Studies | Rijnsdorp A.D.,Wageningen University | And 4 more authors.
Molecular Ecology | Year: 2011

Heavy fishing and other anthropogenic influences can have profound impact on a species' resilience to harvesting. Besides the decrease in the census and effective population size, strong declines in mature adults and recruiting individuals may lead to almost irreversible genetic changes in life-history traits. Here, we investigated the evolution of genetic diversity and effective population size in the heavily exploited sole (Solea solea), through the analysis of historical DNA from a collection of 1379 sole otoliths dating back from 1957. Despite documented shifts in life-history traits, neutral genetic diversity inferred from 11 microsatellite markers showed a remarkable stability over a period of 50 years of heavy fishing. Using simulations and corrections for fisheries induced demographic variation, both single-sample estimates and temporal estimates of effective population size (N e) were always higher than 1000, suggesting that despite the severe census size decrease over a 50-year period of harvesting, genetic drift is probably not strong enough to significantly decrease the neutral diversity of this species in the North Sea. However, the inferred ratio of effective population size to the census size (N e/N c) appears very small (10 -5), suggesting that overall only a low proportion of adults contribute to the next generation. The high N e level together with the low N e/N c ratio is probably caused by a combination of an equalized reproductive output of younger cohorts, a decrease in generation time and a large variance in reproductive success typical for marine species. Because strong evolutionary changes in age and size at first maturation have been observed for sole, changes in adaptive genetic variation should be further monitored to detect the evolutionary consequences of human-induced selection. © 2011 Blackwell Publishing Ltd.


Mollet F.M.,Institute for Marine Resources and Ecological Studies | Mollet F.M.,International Institute For Applied Systems Analysis | Ernande B.,International Institute For Applied Systems Analysis | Ernande B.,French Research Institute for Exploitation of the Sea | And 4 more authors.
Oikos | Year: 2010

We present a new methodology to estimate rates of energy acquisition, maintenance, reproductive investment and the onset of maturation (four-trait estimation) by fitting an energy allocation model to individual growth trajectories. The accuracy and precision of the method is evaluated on simulated growth trajectories. In the deterministic case, all life history parameters are well estimated with negligible bias over realistic parameter ranges. Adding environmental variability reduces precision, causes the maintenance and reproductive investment to be confounded with a negative error correlation, and tends, if strong, to result in an underestimation of the energy acquisition and maintenance and an overestimation of the age and size at the onset of maturation. Assuming a priori incorrect allometric scaling exponents also leads to a general but fairly predictable bias. To avoid confounding in applications we propose to assume a constant maintenance (three-trait estimation), which can be obtained by fitting reproductive investment simultaneously to size at age on population data. The results become qualitatively more robust but the improvement of the estimate of the onset of maturation is not significant. When applied to growth curves back-calculated from otoliths of female North Sea plaice Pleuronectes platessa, the four-trait and three-trait estimation produced estimates for the onset of maturation very similar to those obtained by direct observation. The correlations between life-history traits match expectations. We discuss the potential of the methodology in studies of the ecology and evolution of life history parameters in wild populations. © 2009 Oikos.


Rijnsdorp A.D.,Institute for Marine Resources and Ecological Studies | Rijnsdorp A.D.,Wageningen University | Van Overzee H.M.J.,Institute for Marine Resources and Ecological Studies | Poos J.J.,Institute for Marine Resources and Ecological Studies
Marine Ecology Progress Series | Year: 2012

As a contribution to the ecosystem approach to fisheries management, we estimated the effects of spawning closures on stock status, ecosystem impacts and economic performance. We focused on the flatfish fishery in the North Sea and explored how spawning closures for plaice and sole contribute to sustainable management of 4 target species (sole, plaice, turbot and brill). Seasonal patterns in fishing effort and catchability by age group and area were estimated to quantify the effect of different spawning closure scenarios on the selection pattern. The scenario performance was evaluated using indicators of stock status (spawning stock biomass), economic performance of the fishery (yield, revenue) and ecosystem impact (discards, bycatch of cod and rays, seabed integrity, fisheries-induced evolution). In a single-species context, spawning closures may be beneficial for the target species, while in a mixed fisheries and ecosystem context, negative effects may occur. A spawning closure for plaice combines positive effects on the plaice stock and the revenue with reductions of the negative impact for several ecosystem indicators and only a small negative effect on sea bed integrity. The effects did not differ when evaluated at current levels of effort or at maximum sustainable yield (MSY) effort. Tailor-made solutions are required that need to be developed in stakeholder consultation to trade-off the ecological and economic objectives. Mixed-species MSY was lower than the sum of the single-species MSYs. © 2012 Inter-Research.

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